Unhealthy (101+) AQI Cities
0 US cities have a 5-year median AQI in the unhealthy range. Air quality is unhealthy for sensitive groups and may affect the general population.
What "Unhealthy" AQI Actually Means
An AQI above 100 falls into the EPA's "Unhealthy for Sensitive Groups" category and progressively into "Unhealthy" (151+), "Very Unhealthy" (201+), and "Hazardous" (301+). At AQI 101+, sensitive groups will start to feel symptoms; at AQI 151+, the general population will too; at AQI 201+, the EPA recommends everyone limit outdoor activity. Cities listed here have a 5-year median AQI in this elevated range — meaning the typical day, not just the worst day, falls into Unhealthy territory.
Everyone, in proportion to baseline risk. Sensitive groups — children, pregnant women, older adults, people with asthma, COPD, heart disease, or diabetes — should treat AQI alerts as essential daily input. Healthy adults will start feeling effects (eye/throat irritation, slight breathing difficulty during exercise) on the worst days and should plan accordingly. People with active cancer treatment, recent surgery, or compromised immunity face the highest incremental risk.
What Unhealthy AQI Means for Daily Life
On flagged days, sensitive groups should avoid outdoor exertion and keep windows closed. Schools in these areas often run "indoor recess" protocols and cancel outdoor sports practices when AQI exceeds 150. Outdoor workers (construction, agriculture, landscaping) face the highest occupational exposure and should rotate tasks, take indoor breaks, and consider N95/KN95 respirators when conditions warrant.
Long-Term Health Effects
Long-term residence in cities that average Unhealthy AQI is associated with substantial increases in asthma incidence, lung cancer risk, cardiovascular mortality, and all-cause mortality. The Harvard Six Cities Study and follow-up research consistently find life-expectancy reductions of 1-3 years for residents of the most polluted U.S. metros compared to the cleanest. Children growing up in these areas show measurably reduced lung function as adults — an effect that does not fully recover even after relocation.
How to Protect Your Health
Indoor air quality matters most when outdoor air is consistently bad. A HEPA air cleaner sized to your living space (bedroom + family room minimum) can cut indoor PM2.5 by 80%+ when windows are kept closed. Mechanical filtration in HVAC systems should run MERV-13 or better. On the worst days, an N95 or KN95 respirator provides meaningful protection during outdoor commutes (surgical masks do not). For chronic conditions, work with a pulmonologist or cardiologist on a personalized exposure plan.
Why Some Cities End Up in the Unhealthy Range
Cities in the Unhealthy range typically share one of three patterns: California Central Valley geography (pollution trapped between mountain ranges with limited ventilation), wildfire smoke exposure (increasingly the West), or concentrated industrial and freight corridors (parts of the Ohio Valley, Houston ship channel, port-adjacent neighborhoods). The 5-year median puts these cities in elevated territory, but the daily picture often swings between Moderate and Very Unhealthy depending on weather and fire activity.
All Unhealthy AQI Cities
| City | State | 5yr Avg AQI | Grade | Trend | Worst Pollutant |
|---|
Frequently Asked Questions
An AQI above 100 falls into the EPA's "Unhealthy for Sensitive Groups" category and progressively into "Unhealthy" (151+), "Very Unhealthy" (201+), and "Hazardous" (301+). At AQI 101+, sensitive groups will start to feel symptoms; at AQI 151+, the general population will too; at AQI 201+, the EPA recommends everyone limit outdoor activity. Cities listed here have a 5-year median AQI in this elevated range — meaning the typical day, not just the worst day, falls into Unhealthy territory.
0 of 1,020 monitored US cities have a 5-year average AQI in the unhealthy range (101-500). That is 0.0% of the EPA-monitored cities tracked here.
On flagged days, sensitive groups should avoid outdoor exertion and keep windows closed. Schools in these areas often run "indoor recess" protocols and cancel outdoor sports practices when AQI exceeds 150. Outdoor workers (construction, agriculture, landscaping) face the highest occupational exposure and should rotate tasks, take indoor breaks, and consider N95/KN95 respirators when conditions warrant.
Long-term residence in cities that average Unhealthy AQI is associated with substantial increases in asthma incidence, lung cancer risk, cardiovascular mortality, and all-cause mortality. The Harvard Six Cities Study and follow-up research consistently find life-expectancy reductions of 1-3 years for residents of the most polluted U.S. metros compared to the cleanest. Children growing up in these areas show measurably reduced lung function as adults — an effect that does not fully recover even after relocation.
Indoor air quality matters most when outdoor air is consistently bad. A HEPA air cleaner sized to your living space (bedroom + family room minimum) can cut indoor PM2.5 by 80%+ when windows are kept closed. Mechanical filtration in HVAC systems should run MERV-13 or better. On the worst days, an N95 or KN95 respirator provides meaningful protection during outdoor commutes (surgical masks do not). For chronic conditions, work with a pulmonologist or cardiologist on a personalized exposure plan.
Cities in the Unhealthy range typically share one of three patterns: California Central Valley geography (pollution trapped between mountain ranges with limited ventilation), wildfire smoke exposure (increasingly the West), or concentrated industrial and freight corridors (parts of the Ohio Valley, Houston ship channel, port-adjacent neighborhoods). The 5-year median puts these cities in elevated territory, but the daily picture often swings between Moderate and Very Unhealthy depending on weather and fire activity.
/methodology
Source: EPA Outdoor Air Quality Data, 2026.